java实现大文件下载，基于http方式，控件神马的就不说了。
思路：下载文件无非要读取文件然后写文件，主要这两个步骤，主要难点：
1.读文件，就是硬盘到内存的过程，由于jdk内存限制，不能读的太大。
2.写文件，就是响应到浏览器端的过程，http协议是短链接，如果写文件太慢，时间过久，会造成浏览器死掉。

知识点：

1.org.apache.http.impl.client.CloseableHttpClient  模拟httpClient客户端发送http请求，可以控制到请求文件的字节位置。
2.BufferedInputStream都熟悉，用它接受请求来的流信息缓存。
3.RandomAccessFile文件随机类，可以向文件写入指定位置的流信息。

基于以上信息，我的实现思路就是首先判断下载文件大小，配合多线程分割定制http请求数量和请求内容，响应到写入到RandomAccessFile指定位置中。在俗点就是大的http分割成一个个小的http请求，相当于每次请求一个网页。

废话不说，上代码。

DownLoadManagerTest类：

package xxxx;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.CountDownLatch;
import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.task.TaskExecutor;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.AbstractTransactionalJUnit4SpringContextTests;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

/**
 * 
 * 文件下载管理类
 */
@RunWith(SpringJUnit4ClassRunner.class)
@ActiveProfiles("test")
@ContextConfiguration(locations={"classpath:test/applicationContext.xml"})
public class DownLoadManagerTest extends AbstractTransactionalJUnit4SpringContextTests{
	
	private static final Logger LOGGER = LoggerFactory.getLogger(DownLoadManagerTest.class);

	/**
	 * 
	 * 每个线程下载的字节数
	 */
	private long unitSize = 1000 * 1024;
	
	@Autowired
	private TaskExecutor taskExecutor;
	
	private CloseableHttpClient httpClient;
	
	private Long starttimes;
	
	private Long endtimes;
    
    @Before
    public void setUp() throws Exception{
    	starttimes = System.currentTimeMillis();
        System.out.println("测试开始....");
    }
    
    @After
    public void tearDown() throws Exception{
    	endtimes = System.currentTimeMillis();
        System.out.println("测试结束!!");
        System.out.println("********************");
        System.out.println("下载总耗时:"+(endtimes-starttimes)/1000+"s");
        System.out.println("********************");
    }

	public DownLoadManagerTest() {
		System.out.println("初始化测试类....");
		PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
		cm.setMaxTotal(100);
		httpClient = HttpClients.custom().setConnectionManager(cm).build();
		
	}

	/**
	 * 
	 * 启动多个线程下载文件
	 */
	@Test
	public void  doDownload() throws IOException {

		String remoteFileUrl="http://{host}:{port}/{project}/xx.xml";
		String localPath="E://test//";
		
		String fileName = new URL(remoteFileUrl).getFile();

		System.out.println("远程文件名称："+fileName);
		fileName = fileName.substring(fileName.lastIndexOf("/") + 1,
				fileName.length()).replace("%20", " ");
		System.out.println("本地文件名称："+fileName);
		long fileSize = this.getRemoteFileSize(remoteFileUrl);

		this.createFile(localPath+System.currentTimeMillis()+fileName, fileSize);

		Long threadCount = (fileSize/unitSize)+(fileSize % unitSize!=0?1:0);
		long offset = 0;
		
		CountDownLatch end = new CountDownLatch(threadCount.intValue());
		// 如果远程文件尺寸小于等于unitSize
		if (fileSize <= unitSize) {

			DownloadThreadTest downloadThread = new DownloadThreadTest(remoteFileUrl,
					localPath+fileName, offset, fileSize,end,httpClient);

			taskExecutor.execute(downloadThread);

		} else {
			// 如果远程文件尺寸大于unitSize
			for (int i = 1; i < threadCount; i++) {
				DownloadThreadTest downloadThread = new DownloadThreadTest(
				remoteFileUrl, localPath+fileName, offset, unitSize,end,httpClient);
				taskExecutor.execute(downloadThread);
				offset = offset + unitSize;

			}
			// 如果不能整除，则需要再创建一个线程下载剩余字节
			if (fileSize % unitSize != 0) {
				DownloadThreadTest downloadThread = new DownloadThreadTest(remoteFileUrl, localPath+fileName, offset, fileSize - unitSize * (threadCount-1),end,httpClient);
				taskExecutor.execute(downloadThread);
			}
		}
		try {
			end.await();
		} catch (InterruptedException e) {
			LOGGER.error("DownLoadManager exception msg:{}",ExceptionUtils.getFullStackTrace(e));
			e.printStackTrace();
		}
//		System.out.println("111111");
		LOGGER.debug("下载完成！{} ",localPath+fileName);
		//return localPath+fileName;
	}

	/**
	 * 
	 * 获取远程文件尺寸
	 */
	private long getRemoteFileSize(String remoteFileUrl) throws IOException {
		long fileSize = 0;
		HttpURLConnection httpConnection = (HttpURLConnection) new URL(
		remoteFileUrl).openConnection();
		httpConnection.setRequestMethod("HEAD");
		int responseCode = httpConnection.getResponseCode();
		if (responseCode >= 400) {
			LOGGER.debug("Web服务器响应错误!");
			return 0;
		}

		String sHeader;
		for (int i = 1;; i++) {
			sHeader = httpConnection.getHeaderFieldKey(i);
			if (sHeader != null && sHeader.equals("Content-Length")) {
				System.out.println("文件大小ContentLength:"
						+ httpConnection.getContentLength());
				fileSize = Long.parseLong(httpConnection
						.getHeaderField(sHeader));
				break;
			}
		}
		return fileSize;
	}

	/**
	 * 
	 * 创建指定大小的文件
	 */
	private void createFile(String fileName, long fileSize) throws IOException {
		File newFile = new File(fileName);
		RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
		raf.setLength(fileSize);
		raf.close();
	}

	public TaskExecutor getTaskExecutor() {
		return taskExecutor;
	}

	public void setTaskExecutor(TaskExecutor taskExecutor) {
		this.taskExecutor = taskExecutor;
	}
}

DownloadThreadTest类：

package xxxx;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.CountDownLatch;
import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 
 * 负责文件下载的类
 */
public class DownloadThreadTest extends Thread {

	private static final Logger LOGGER = LoggerFactory
			.getLogger(DownloadThreadTest.class);

	/**
	 * 
	 * 待下载的文件
	 */
	private String url = null;

	/**
	 * 
	 * 本地文件名
	 */
	private String fileName = null;

	/**
	 * 
	 * 偏移量
	 */
	private long offset = 0;

	/**
	 * 
	 * 分配给本线程的下载字节数
	 */
	private long length = 0;
	private CountDownLatch end;
	private CloseableHttpClient httpClient;
	private HttpContext context;

	/**
	 * 
	 * @param url 下载文件地址
	 * 
	 * @param fileName 另存文件名
	 * 
	 * @param offset  本线程下载偏移量
	 * 
	 * @param length  本线程下载长度
	 * 
	 * @author Angus.wang
	 * 
	 * */
	public DownloadThreadTest(String url, String file, long offset, long length,
			CountDownLatch end, CloseableHttpClient httpClient) {
		this.url = url;
		this.fileName = file;
		this.offset = offset;
		this.length = length;
		this.end = end;
		this.httpClient = httpClient;
		this.context = new BasicHttpContext();
		LOGGER.debug("偏移量=" + offset + ";字节数=" + length);
	}

	public void run() {
		try {
			HttpGet httpGet = new HttpGet(this.url);
			httpGet.addHeader("Range", "bytes=" + this.offset + "-"
					+ (this.offset + this.length - 1));
			CloseableHttpResponse response = httpClient.execute(httpGet,
					context);
			BufferedInputStream bis = new BufferedInputStream(response
					.getEntity().getContent());
			byte[] buff = new byte[1024];
			int bytesRead;
			File newFile = new File(fileName);
			RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
			while ((bytesRead = bis.read(buff, 0, buff.length)) != -1) {
				raf.seek(this.offset);
				raf.write(buff, 0, bytesRead);
				this.offset = this.offset + bytesRead;
			}
			raf.close();
			bis.close();
		} catch (ClientProtocolException e) {
			LOGGER.error("DownloadThread exception msg:{}",ExceptionUtils.getFullStackTrace(e));
		} catch (IOException e) {
			LOGGER.error("DownloadThread exception msg:{}",ExceptionUtils.getFullStackTrace(e));
		} finally {
			end.countDown();
			LOGGER.info(end.getCount() + " is go on!");
			System.out.println(end.getCount() + " is go on!");
		}
	}
}

application.xml

<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
		<!-- 线程池活跃的线程数 -->
		<property name="corePoolSize" value="5" />
		<!-- 线程池最大活跃的线程数 -->
		<property name="maxPoolSize" value="10" />
		<!-- 队列的最大容量 -->
		<property name="queueCapacity" value="600" />
	</bean>
	<bean id="downLoadManager"
		class="xx.DownLoadManagerTest">
		<property name="taskExecutor" ref="taskExecutor" />
	</bean>

测试运行，500M,我这网速得半个小时左右。要想下载更大的文件，只要jdk内存够大，就无限更改队列最大容量吧。

如果不同意见，欢迎各位大神指正。

转载：https://my.oschina.net/zmf/blog/336961

计算不同用户的下载进度

import java.io.*;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.HashMap;

public class ProgressBarThread implements Runnable {

    private ArrayList<Integer> proList = new ArrayList<Integer>();
    private int progress;//当前进度
    private int totalSize;//下载文法总大小
    private boolean run = true;
    private int showProgress;
    public static HashMap<String, Integer> progressMap = new HashMap<>();//各用户的下载进度
    public static HashMap<String, Boolean> executeStatusMap = new HashMap<>();//各用户是否下载中
    private Long fileId;
    private String token;

    public ProgressBarThread(int totalSize, Long fileId, String token) {
        this.totalSize = totalSize;
        this.fileId = fileId;
        this.token = token;
        //创建进度条时，将指定用户的执行状态改为true
        executeStatusMap.put(token, true);
    }

    /**
     * @param progress 进度
     */
    public void updateProgress(int progress) {
        synchronized (this.proList) {
            if (this.run) {
                this.proList.add(progress);
                this.proList.notify();
            }
        }
    }

    public void finish() {
        this.run = false;
        //关闭进度条
    }

    @Override
    public void run() {
        synchronized (this.proList) {
            try {
                while (this.run) {
                    if (this.proList.size() == 0) {
                        this.proList.wait();
                    }
                    synchronized (proList) {
                        this.progress += this.proList.remove(0);
                        //更新进度条
                        showProgress = (int) ((new BigDecimal((float) this.progress / this.totalSize).setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue()) * 100);
                        progressMap.put(token + fileId, showProgress);
                        if (showProgress == 100) {
                            //进度100%时将用户的执行状态改为false
                            executeStatusMap.put(token, false);
                        }
                        System.err.println("当前进度："+showProgress+"%");
                    }
                }
                System.err.println("下载完成");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        try {
            File file = new File("C:/Users/mfy/Desktop/蜜雪冰城.pdf");
            FileInputStream fis = new FileInputStream(file);
            FileOutputStream fos = new FileOutputStream("D:/nms/img/蜜雪冰城.pdf");
            ProgressBarThread pbt = new ProgressBarThread((int) file.length(), 1L, "000001");//创建进度条
            new Thread(pbt).start();//开启线程，刷新进度条
            byte[] buf = new byte[1024];
            int size = 0;
            while ((size = fis.read(buf)) > -1) {//循环读取
                fos.write(buf, 0, size);
                pbt.updateProgress(size);//写完一次，更新进度条
            }
            pbt.finish();//文件读取完成，关闭进度条
            fos.flush();
            fos.close();
            fis.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

获取获取下载进度，可以通过webSocket推送，也可以前端定时调用

    public HzRestResult getProgress(String fileId, HttpServletRequest request) {
        String token = request.getHeader("token");
        Integer progress = ProgressBarThread.progressMap.get(token + fileId);
        if (progress == null) {
            return HzRestResult.getFailed("该任务不存在!");
        }
         if(progress.equals(100)){
            //进度100%时清除指定map
            ProgressBarThread.progressMap.remove(token + fileId);
        }
        JSONObject jsonObject = new JSONObject();
        jsonObject.put("fileId", fileId);
        jsonObject.put("token", token);
        jsonObject.put("progress", progress);
        return HzRestResult.getSuccess(jsonObject);
    }